The present application is directed to micro-electro-mechanical methods and devices, and more particularly to such devices and methods for the manufacture of fluid drop ejectors to eject fluid drops such as and biological material, among others.
A MEMS (micro-electro-mechanical system) drop ejector has been disclosed in U.S. patent application Ser. No. 11/863,637 (Publ. No. 2001-0023523), titled “Method Of Fabricating A Micro-Electro-Mechanical Fluid Ejector”, by Kubby et al., filed May 23, 2001, incorporated herein in its entirety.
The Kubby et al. application described a micro-electro-mechanical fluid ejector fabricated by a standard polysilicon surface micro-machine process, which can be batch fabricated at low cost using existing external foundry capabilities. In addition, it is disclosed that the surface micro-machine process is proven to be compatible with integrated micro-electronics, allowing for monolithic integration of the actuator with addressing electronics. A voltage drive mode and a charge drive mode for the power source actuating a deformable membrane is also disclosed.
FIG. 1 shows a cross-sectional view of an electrostatically actuated diaphragm 100 such as disclosed in Kubby et al. in the relaxed state. Substrate 120 is typically a silicon wafer. Insulator layer 130 is typically a thin film of silicon nitride, Si3N4. Conductor 140 acts as the counter or deflector electrode and is typically either a metal or a doped semiconductor film such as polysilicon. Membrane 150 is made from a structural material such as polysilicon, as is typically used in a surface micromachining process. Nipple 152 is attached to a part of membrane 150 and acts to separate the membrane from the conductor when the membrane is pulled down towards the conductor under electrostatic attraction when a voltage or current, as indicated by power source P, is applied between the membrane and the conductor. Actuator chamber (where a fluid may be located) 154 between membrane 150 and substrate 120 can be formed using typical techniques such as are used in surface micromachining. A sacrificial layer, such as chemical vapor deposition (CVD) oxide is deposited, which is then covered over by the structural material that forms the membrane. An opening left in the membrane (not shown) allows the sacrificial layer to be removed in a post-processing etch. A typical etchant for oxide is concentrated hydrofluoric acid (HF). In this processing step, nipple 152 acts to keep the membrane from sticking to the underlying surface when the liquid etchant capillary forces pull it down.
The standard surface micromachining process to manufacture drop ejectors such as shown in FIG. 1, among others, is limited to silicon substrates, thus restricting the size of a device array. In order to implement larger arrays, such as full-page-width ejector using a device array, a new fabrication process is required. It is therefore desirable to provide a method of manufacturing and new devices which allow for large area arrays as well as other improvements.